Abstract: Compared with the traditional static load test method, the self-balanced pile test method has the advantages of convenience, economy and adaptability. However, the method is always controversial. To study the difference and reason of load transfer law between self-balanced and traditional static load test pile methods, the laboratory model tests of self-balanced pile, static pressure pile and uplift pile in granite residual soil under the same boundary condition are carried out. Through the resistance strain gauge attached to one side of the pile body, the strain values of the pile body at different positions under various loads are obtained. Additionally, the ultimate bearing capacity of the single pile, the axial force transfer of the pile body, and the distribution of friction on the side of the pile are analyzed. The results show that: 1) In granite residual soil, the self-balanced upper pile and the uplift pile show “sudden” failure when they reach the ultimate load; 2) The conversion coefficient ? of pile side friction resistance in granite residual soil obtained by the model test is 0.573; 3) The ultimate uplift bearing capacity of single pile measured by two loading methods of bottom support and top pull is equivalent; 4) The load is transferred from loading position to the other end of the pile. For each test pile, the distribution of the relatively larger value of the lateral friction resistance is different. For the self-balancing pile and the uplift pile, the positions are concentrated in the bottom of the pile, and for the static pressure test pile that is concentrated in the middle of the pile body.

Key words: pile test method, self-balance, model test, granite residual soil, load transfer, pile side friction